Control unit for an electric motor, in particular for a fan motor

ABSTRACT

The invention provides a control unit for at least one electric motor, wherein the control unit performs open-loop or closed-loop control of the motor speed of the electric motor in such a way that in the case of control values in specific ranges which are typical of a fault when the setpoint value is being predefined, such a fault being, for example, a line break, a voltage failure or a short circuit, the control unit drives the motor with a predefined setpoint value which differs from the current control value.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority of InternationalPatent Application No. PCT/EP2007/054301, filed on May 3, 2007, whichapplication claims priority to German Patent Application No. 20 2006 007136.9, filed May 4, 2006. The entire text of the priority application inincorporated herein by reference in its entirety.

DESCRIPTION

The invention relates to a control unit for an electric motor. Suchcontrol units are used to perform open-loop or closed-loop control ofthe motor speed. In many cases, in particular in fan applications, themotor speed is lowered according to demand in order to reduce theconsumption of electric power. In the case of a fan, not only the powerdemand but also the flow noise are highly dependent on the motor speed.FIG. 1 shows the shaft power output of the fan motor (1) and the flownoise of the fan (2) as a function of the motor speed. The torque demandof a fan wheel increases to the power of two of the motor speed. As aresult, the shaft power output of the motor even increases to the powerof three of the motor speed. This means that, for example, at half themotor speed the output power of the motor only reaches 12.5% of therated power. The shaft power output even drops below 1% if the motorspeed is less than 21.5% of the rated motor speed. The flow noise (2)has been found empirically to drop to 15 17 dB(A) when the motor speedis halved.

In addition to the energy demand, the noise can therefore also besignificantly reduced if motor-speed-controlled fan motors are used andif open-loop control of the motor speed and therefore of the air line isperformed according to demand. The motor speed of a fan can beinfluenced in different ways as a function of the types of motor used.In the case of direct current motors, open-loop control of the motorspeed is performed by means of the motor voltage. The control unit canpredefine the motor voltage with a clocked voltage converter (chopper)or by means of a controlled rectifier. For universal motors, theamplitude of the alternating voltage can be set by means of a phaseangle controller. In the case of a brushless motor (also referred to asBLDC or electronically commutated motor, referred to as EC motor), thecontrol unit performs the electronic commutation. The control unit canadditionally influence the motor voltage and as a result the motor speedthrough corresponding clocking of the transistors in the commutationelectronics. In the case of asynchronous motors, either the frequencyand the amplitude of the motor voltage are predefined with a frequencyconverter, or in the case of cost-effective systems, in particular inthe case of fan drives, only the motor voltage is changed, for example,by means of a phase angle controller (referred to as slip controller).

The desired motor speed is usually defined by means of superimposedopen-loop control. The setpoint value of the motor speed is oftentransmitted with an analogue value (for example 0 10 V) or with apulse-width-modulated, digital value (PWM). FIG. 2 shows an inputcharacteristic which is typical of fan applications. In this example,the superimposed controller has to output 0 10% of the control signal(x) for the motor to be stationary (nsetp=0). A disadvantage of thismethod is that in the case of faults, for example in the case of a linebreak or a short circuit in the control line, the fan can stop. In thiscase, it is not possible to ensure sufficient cooling, which may lead toa failure of the system. As a result, considerable material damage mayoccur and large losses due to a failure of production.

SUMMARY OF THE INVENTION

The present invention is therefore based on the object of configuringthe input characteristic of the control unit in such a way that in thecase of such a fault the motor continues to operate with a predefinedmotor speed. In the case of a fault such as a line break or a shortcircuit in the control line or in the case of the failure of thesuperimposed controller, the probability is high that the control signalx will record the value 0% or 100%.

According to the invention, the customary input characteristic istherefore changed according to FIG. 2 in such a way that in the case ofinput values in specific ranges, primarily approximately 0% or 100%, thecontroller drives the motor with a predefined setpoint value whichdiffers from the current setpoint value.

In one advantageous embodiment, the controller additionally outputs awarning in the case of such a fault. This warning can be output by meansof a visual or audible signal, by means of an analogue or digitalelectronic signal or by means of a commutation bus, for example, CANbus.

BRIEF SUMMARY OF THE DRAWINGS

In the figures:

FIG. 1 shows the shaft output power of the fan motor and the flow noiseof the fan as a function of the motor speed;

FIG. 2 shows an input characteristic which is typical of fanapplications;

FIG. 3 shows the input characteristic of the control unit in anadvantageous embodiment;

FIG. 4 shows the inventive input characteristic of the control unit if asetpoint value of nsetp=75% is used when such a fault is detected;

FIG. 5 shows the program sequence for implementing the inputcharacteristic curve;

FIG. 6 shows a exemplary circuit, and

FIG. 7 shows a further exemplary circuit with a warning output.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows the input characteristic of the control unit in anadvantageous embodiment. In this example, the superimposed controllermust output 5 10% of the control signal (x) instead of 0 10% in order tostop the motor. In the case of an analogue control signal (0 10 V) thismeans that in the case of a control voltage of 0.5 V to 1 V the motor isstationary (nsetp=0). A control voltage of less than 0.5 V indicates afault (for example a failure of the superimposed controller, a linebreak or a short circuit in the control line). When a setpoint value ispredefined with a PWM controlled digital signal, the motor will bestationary given a control signal of 5 to 10% PWM. A PWM factor of lessthan 5% means a fault. This is the case, for example, if the controlsignal is continuously at a low level (corresponds to 0% PWM). In thiscase, a predefined setpoint value of the motor speed is used. In FIG. 3,this value is for the fault nsetp=100%. For applications such as, forexample, with fans, reliable operation is therefore ensured even in thecase of a fault in the transferring of setpoint values. Although in fanapplications, the power and noise are not reduced when such a faultoccurs, sufficient cooling is ensured.

DETAILED DESCRIPTION OF THE INVENTION

A setpoint value which differs from the maximum (100%) setpoint value ofthe motor speed can also be used in the event of a fault. In some cases,a reduced motor speed is sufficient for cooling in a normal situation,and the maximum motor speed (100%) is provided only for specificexceptional situations, for example for the failure of one of the fanswhich operate in parallel. FIG. 4 shows the inventive inputcharacteristic of the control unit if a setpoint value of nsetp=75% isused for the detected fault. This value is therefore used if the controlsignal assumes x values in the ranges 0 5% and 95% 100%.

In order to implement an input characteristic curve according to FIG. 4,the analogue control signal can firstly be converted into a digitalvalue using an analogue/digital converter. The signal is then furtherprocessed in digital form. In one advantageous refinement of theinvention, this can be carried out by means of a programmable componentsuch as a microprocessor, digital signal processor (DSP) ormicrocontroller. The programme sequence for implementing the inputcharacteristic curve is illustrated in FIG. 5.

In a further refinement of the invention, the input characteristic curveis implemented using an electronic analogue circuit. FIG. 6 shows anexemplary circuit for this. This circuit is composed of four analoguecomparators (K1 to K4), two operational amplifiers (V1, V2), two digitalNAND gates, and of an analogue multiplexer (MUX). The comparatorscompare the control signal X with the voltage values at thediscontinuities in the input characteristic according to FIG. 4, that isto say with 0.5 V, 1 V, 9 V and 9.5 V. These voltages are produced herefrom the 10 V supply voltage with a resistor series. The output signalsof the comparators are further processed with the NAND gates and controlthe analogue multiplexer, as is shown by the following table.

TABLE 1 Control signal X K4 K3 K2 K1 A1 A0 Y 0 . . . 0.5 V 1 1 0 0 1 1 F0.5 . . . 1 V 1 1 0 1 1 0  0 V 1 . . . 9 V 1 1 1 1 0 0 9 X − 1 V 8 9 . .. 9.5 V 1 0 1 1 0 1 10 V 9.5 . . . 10 V 0 0 1 1 1 1 F

F is here the predefined setpoint value for the fault. If this value is,for example, 75%, as in FIG. 4, 7.5 V has to be connected here.

This circuit can be supplemented with a warning output (W), asillustrated in FIG. 7. In a normal situation this output supplies alogic “1” and in the case of a fault it supplies a logic “0”. Thiswarning is output if the control signal X assumes values lower than 0.5V or higher than 9.5 V.

The control unit according to the invention can form a separate unit orcan be integrated into the motor housing or into the terminal box of themotor so that motor and control unit form one mechanical unit. Thesolution according to the invention can also advantageously be used incompact fans where control unit and motor are integrated parts of thecompact fan. The solution according to the invention can, however, beused not only in fans, blowers and pumps but also in any application inwhich in the event of a fault it is more favourable to operate the motorwith a predefined motor speed than to switch off the motor.Correspondingly, the invention is not only limited to the illustratedand described exemplary embodiments but rather also comprises allembodiments of like effect within the sense of the invention.

As one example, a brushless DC motor that incorporates aspects of theinvention disclosed herein can be used to spin one or more hard disks inoperative relation to at least one read/write head inside of a cleanroom environment that is manufactured to HDD industry contaminationstandards. As another example, the motors disclosed herein can be usedto move storage media in other information storage devices such as, forexample, an optical disk drive, a magneto-optical disk drive, a tapedrive or a VCR.

1. Control unit for at least one electric motor, wherein the controlunit performs open-loop or closed-loop control of the motor speed of theelectric motor in such a way that in the case of control values incertain ranges which are typical of a fault when the setpoint value isbeing predefined, such a fault being, for example, a line break, avoltage failure or a short circuit, the control unit drives the motorwith a predefined setpoint value which differs from the current controlvalue.
 2. Control unit according to claim 1, wherein in the case ofcontrol values in specific ranges which are typical of a fault when thesetpoint value is being predefined, such a fault being, for example, aline break, a voltage failure or a short circuit, the control unitoutputs a warning.
 3. Control unit according to claim 1, wherein thecontrol value is predefined using an analogue voltage signal, and in thecase of voltages which can occur in the case of typical faults such aszero voltage or a signal voltage which is identical to the supplyvoltage, the motor operates with a predefined setpoint value.
 4. Controlunit according to claim 1, wherein the control value is predefined usinga modulated digital signal such as a pulse-width-modulated signal, andin the case of modulations which can occur in the case of typical faultssuch as 0% or 100% modulation, the motor operates with a predefinedsetpoint value.
 5. Control unit according to claim 1, wherein thepredefined setpoint value corresponds to the maximum setpoint value(100%).
 6. Control unit according to claim 1, wherein the motor iscommutated electronically, and the control unit performs the function ofthe electronic commutation.
 7. Control unit for at least one electricmotor according to claim 1, wherein the electric motor drives a fan or apump.
 8. Control unit for an electric motor according to claim 1,wherein the control unit forms a mechanical unit with the motor. 9.Control unit according to claim 8, wherein the control unit isintegrated into the motor housing.
 10. Control unit according to claim8, wherein the control unit is integrated into the terminal box of themotor.
 11. Control unit for an electric motor according to claim 1,wherein the control unit and the motor are parts of a compact fan. 12.Control unit according to claim 1, characterized in that the setpointvalue operates with an electronic analogue circuit.
 13. Control unitaccording to claim 1, wherein the control value is converted into adigital value using an analogue/digital converter, and the control valueis further processed in digital form.
 14. Control unit according toclaim 13, wherein the digital control value is processed with aprogrammable component such as a microprocessor, digital signalprocessor (DSP) or microcontroller.